Module 21: Security & Best Practices

Overview

This final module covers JavaScript security fundamentals, performance optimization, and industry best practices for building production-ready applications.

Learning Objectives

By the end of this module, you will be able to:

• •Understand and prevent common JavaScript security vulnerabilities
• •Implement secure coding practices
• •Optimize JavaScript performance
• •Apply design patterns and best practices
• •Write clean, maintainable code

Module Structure

Module-21-Security-Best-Practices/
├── README.md
├── 21.1-Security-Fundamentals/
│   ├── README.md           # XSS, CSRF, injection attacks
│   ├── examples.js         # Security vulnerability demos
│   └── exercises.js        # Security practice exercises
├── 21.2-Secure-Coding/
│   ├── README.md           # Input validation, sanitization
│   ├── examples.js         # Secure coding patterns
│   └── exercises.js        # Security implementation
├── 21.3-Performance-Optimization/
│   ├── README.md           # Optimization strategies
│   ├── examples.js         # Performance patterns
│   └── exercises.js        # Performance exercises
├── 21.4-Design-Patterns/
│   ├── README.md           # Common JS design patterns
│   ├── examples.js         # Pattern implementations
│   └── exercises.js        # Pattern practice
└── 21.5-Code-Organization/
    ├── README.md           # Clean code principles
    ├── examples.js         # Organization examples
    └── exercises.js        # Refactoring exercises

Topics Covered

21.1 Security Fundamentals

• •Cross-Site Scripting (XSS) prevention
• •Cross-Site Request Forgery (CSRF) protection
• •Injection attack prevention
• •Content Security Policy (CSP)
• •Security headers

21.2 Secure Coding

• •Input validation and sanitization
• •Output encoding
• •Authentication best practices
• •Secure data handling
• •Cryptography basics

21.3 Performance Optimization

• •DOM optimization techniques
• •Memory management
• •Lazy loading and code splitting
• •Caching strategies
• •Web Worker usage

21.4 Design Patterns

• •Creational patterns (Factory, Singleton, Builder)
• •Structural patterns (Adapter, Decorator, Facade)
• •Behavioral patterns (Observer, Strategy, Command)
• •Module patterns
• •Async patterns

21.5 Code Organization

• •Clean code principles
• •SOLID in JavaScript
• •Code documentation
• •Project structure
• •Maintainability patterns

Security Quick Reference

┌───────────────────────────────────────────────────────────────────────┐
│                    Common Security Vulnerabilities                     │
├────────────────┬──────────────────────────────────────────────────────┤
│ Vulnerability  │ Prevention                                           │
├────────────────┼──────────────────────────────────────────────────────┤
│ XSS            │ Escape output, CSP, avoid innerHTML                  │
│ CSRF           │ CSRF tokens, SameSite cookies                        │
│ SQL Injection  │ Parameterized queries, ORM                           │
│ Code Injection │ Never eval() user input, sandbox                     │
│ Path Traversal │ Validate/sanitize file paths                         │
│ Open Redirect  │ Whitelist allowed redirect URLs                      │
│ Sensitive Data │ HTTPS, encryption, secure storage                    │
└────────────────┴──────────────────────────────────────────────────────┘

Performance Quick Reference

┌───────────────────────────────────────────────────────────────────────┐
│                    Performance Optimization Areas                      │
├────────────────┬──────────────────────────────────────────────────────┤
│ Area           │ Techniques                                           │
├────────────────┼──────────────────────────────────────────────────────┤
│ DOM            │ Batch updates, virtual DOM, requestAnimationFrame    │
│ Memory         │ Avoid leaks, proper cleanup, weak references         │
│ Loading        │ Lazy load, code split, defer/async scripts           │
│ Runtime        │ Memoization, debounce/throttle, Web Workers          │
│ Network        │ Caching, compression, CDN, HTTP/2                    │
│ Rendering      │ CSS containment, avoid reflows, GPU acceleration     │
└────────────────┴──────────────────────────────────────────────────────┘

Design Patterns Overview

┌───────────────────────────────────────────────────────────────────────┐
│                        Design Pattern Categories                       │
├───────────────────────────────────────────────────────────────────────┤
│                                                                        │
│  CREATIONAL                STRUCTURAL              BEHAVIORAL          │
│  ┌──────────────┐         ┌──────────────┐        ┌──────────────┐   │
│  │ Factory      │         │ Adapter      │        │ Observer     │   │
│  │ Singleton    │         │ Decorator    │        │ Strategy     │   │
│  │ Builder      │         │ Facade       │        │ Command      │   │
│  │ Prototype    │         │ Proxy        │        │ State        │   │
│  │ Module       │         │ Composite    │        │ Iterator     │   │
│  └──────────────┘         └──────────────┘        └──────────────┘   │
│                                                                        │
└───────────────────────────────────────────────────────────────────────┘

Prerequisites

Before starting this module, you should be comfortable with:

• •Core JavaScript (ES6+)
• •Asynchronous programming
• •DOM manipulation
• •Object-oriented programming
• •Module systems

Running Examples

# Run examples
node 21.x-Topic/examples.js

# Run exercises
node 21.x-Topic/exercises.js

Further Learning

Security Resources

• •OWASP Top 10
• •Content Security Policy (CSP) documentation
• •MDN Web Security guidelines

Performance Resources

• •Chrome DevTools documentation
• •Lighthouse performance audits
• •Web Vitals metrics

Design Patterns

• •"JavaScript Design Patterns" by Addy Osmani
• •"Clean Code in JavaScript" by James Padolsey
• •Gang of Four patterns adapted to JS